Vibrationless percussive tool



June 14, 1966 Q. LEAVELL VIBRATIONLESS PERCUSSIVE TOOL Filed Nov. 27,1962 FIG.2

United States Patent 3,255,832 VIBRATIONLESS PERCUSSIVE TOOL CharlesLeavell, 206 S. Fair-field Ave., Lombard, Ill. Filed Nov. 27, 1962, Ser.No. 240,316 7 Claims. 01. 173-433 .This invention is concerned with theproblem of eliminating vibration in tripartite vibratile structurescomprising (1) a first desirably or unavoidably vibrating body, (2) asecond body in which the occurrence of vibration is objectionable, and(3) connecting structure accomplishing a necessary transmission of forcebetween such two bodies; and it rel-ates in particular to vibrationlesspercussive tools of the type disclosed in my issued Patents Nos.3,028,840 and 3,028,841.

g In Patent No. 3,028,841, I disclosed an inventive concept offundamental character generally applicable to an exceedingly widevariety of tripartite vibratile structures for substantially eliminatingthe transmission of vibration between such first and second bodiesthereof While maintaining a necessary transmission of forcetherebetween; and I exemplified such invention in the environment ofpercussive tools because the problems encountered in eliminatingvibration in tools of this class are more difficult of solution thanthose encountered in most other environments. Within this class oftools, the paving breaker was selected for specific considerationbecause it presents perhaps the most difiicult challenge for eliminatingthe transmission of vibration between a first necessarily vibrating bodyand a second body in which the occurrence of vibration is undesirable.

As set forth in the aforementioned patents in considering the pavingbreaker as an exemplary percussive tool, the typical paving breakerincludes a casing defining an axially extending cylinder, a hammer orpiston reciprocable within the cylinder, and a steel spike or workmember slidably carried by the casing for limited axial movement withrespect thereto and which is adapted to receive impact from the hammer(usually through an anvil or tappet interposed therebetween) at one endof the reciprocatory stroke thereof. The impact transmitted by thehammer to the spike is delivered thereby to a concrete slab or otherwork material to break or demolish the same, and the hammer isreciprocated within its cylinder by the alternate application ofpressure fluid to the opposite ends or faces of the hammer.

In such usual paving breaker, the charges of compressed air alternatelyadmitted into the opposite ends of the cylinder to respectivelyreciprocate the hammer in directions toward and away from the spike areeach reactively applied against transverse surfaces defining the endclosures of the cylinder, and as aconsequence thereof, the casing ismoved or vibrated in opposite directions along the axis of reciprocationof the hammer. In many tool structures, the hammer is reciprocatedthrough approximately 1,200 cycles each minute, and consequently, thepressure forces reacting alternately against opposite ends of the casingcylinder introduce a violent and objectionable vibration into thecasing. Thus, in the usual paving breaker, the compressed air pressureforce reacting alternately against opposite ends of'the casing cylinderdefines the aforementioned connecting structure accomplishing anecessary transmission of force between the hammer, which is a desirablyor unavoidably vibrating body, and the casing, which is a body in whichthe occurrence of vibration is objectionable.

In Patent No. 3,028,841, the invention disclosed for eliminating thevibration ordinarily introduced into the casing of such a percussivetool by the pressure forces reactively applied against the ends of thecasing cylinder in actuating the hammer, includes means forcounterbalancing such reactive forces by the simultaneous applica-3,255,832 Patented June 14, l9fi6 random and irregular recoil forces arefed into the tool structure through the steel spike as a result of thenonhomogeneity of the slab being penetrated thereby, and because suchrecoil forces tend to cause the oscillator to migrate toward one end ofits cylinder and to impact the end closure thereof, which is anundesirable condition in that it would reintroduce vibration into thecasing, the invention is also concerned with avoiding such a conditionof impact relation between the oscillator and end of its cylinder; andthis result is accomplished by stabl-izing the mean position of theoscillator by means of an automatic control system that includes apneumatic column operative between the oscillator structure and one endof its cylinder. This pneumatic column defines a force-transmittinglinkage or connecting structure coupling the necessarily vibratingoscillator and cylinder therefor in which the occurrence of vi ration isobjectionable; and the automatic control system also includes anarrangement for maintaining the force defined by such pneumatic columnrelatively constant during any one cycle of reciprocation of theoscillator, and it further includes feedback control means forregulatively adjusting the value of such relatively constant forceduring a plurality of reciprocations of the oscillator to positionallystablize the same as aforesaid in order to maintain it in a condition ofintermediacy relative to the ends of its cylinder.

In Patent No. 3,028,841, the axis of oscillation or reciprocation of theoscillatory mass member comprised by the pressure-force counterbalancingsystem is angularly offset from the axis of reciprocation of theblow-striking hammer of the paving breaker which gives rise to the useof a special orientation for such axes identified as a condition ofcopivotality (see such patent for an explana tion thereof); and inPatent No. 3,028,840, the need for or desirability of using such specialcondition is obviated by dividing the unitary oscillatory mass memberand its assocated system intotwo separate but substantially identicaloscillator components each with its own related system and disposing thesame symmetrically with respect to the hammer and its axis ofreciprocation. Correspondingly, the automatic control system of suchtwin oscillator tool is divided into two individual systems respectivelyassociated with the two oscillator components.

The present invention is concerned with vi brationless paving breakersof the type disclosed in the aforementioned patents and departs from theteachings thereof in that a single oscillator or oscillatory mass memberof unitary annular construction, concentrically related to thehammer-piston and its cylinder, is employed instead of the plurality ofoscillators disclosed in Patent No. 3,028,840 and in place of theangularly offset oscillator disclosed in Patent No. 3,028,841.Advantages realized from such construction include, among others,mechanical simplification of the tool, eliminating the duplication ofparts in multiple-oscillator tools and thereby reducing manufacturingcosts, generally reducing the diameter of the tool and specificallyminimizing such dimension by locating the annular oscillator about areduced diameter portion of the fronthead of the tool, and otherwiseproviding a conveniently handled and easily manipulated vibrationlesspercussive tool.

The precussive tool of the present invention also has as an advantage ananvil and hammer-piston arrangement in which a very eflicient andsubstantially complete transfor of blow-striking energy is eliected fromthe hammer-piston to the anvil upon impact therebetween. Ad-

3 ditional objects and advantages of the invention will become apparentas the specification develops.

Embodiments of the invention are illustrated in the accompanyingdrawings in which:

FIGURE 1 is a longitudinal sectional view of a paving breaker embodyingthe invention taken generally along the axis of reciprocation of thehammer-piston thereof;

FIGURE 2 is a transverse sectional view taken along the plane 22 ofFIGURE 1; and

FIGURE 3 is a transverse sectional view generally similar to that ofFIGURE 2 but illustrating a slightly modified construction.

The tool structure illustrated in FIGURE 1 is a pneumatically actuatedpaving breaker comprising a casing composition 11 providing a maincylinder 12 having therein a pneumatically-actuated free-piston hammeror mass member 13. The casing 11 is equipped with handles T, andprovides an exhaust composition 14 to atmosphere communicating with thecylinder 12 intermediate the ends thereof. Such exhaust composition 14includes a plurality of ports 14a opening into the cylinder 12' andcommunicating through a collection space with passage structure 14b thatopens into an outlet 140 provided by the tool casing. The upper end ofthe cylinder 12 is occupied by a conventional pressure-responsive valvecomposition 12' operative to direct the flow of gaseous fluid (such ascompressed air) alternately to the lower and upper end portions of thecylinder to energize the reciprocatory cycle of the hammer 13 byselectively applying upwardly and downwardly active axial pressureforces alternately to the lower surface 13a and to the upper surface 13bthereof.

Compressed air is supplied to the valve composition 12' from acompressor or other suitable source (not shown) through a hose H coupledto the handle T. A passage 12" in such handle communicates at one endwith the hose and at its other end opens into a manifold chamber 120that connects with a collection space 12d through a plurality of ports126. A spring-biased trigger or valve 12 is disposed in the passage 12to control the supply of compressed air to the valve composition 12',and in the position shown, the trigger 12 is depressed so that thepassage 12" is open. The valve composition 12' has a pair of separateoutlets, one of which is denoted with the numeral 12g and connects witha passage 17a through an annular channel 1211 to supply compressed airto the cylinder space below the hammer 13, and the other of which isdenoted with the numeral Hi and communicates directly with the cylinderspace above the hammer 13.

The bottom cylinder head area facing the lower surface 13a of the hammerconsists only of the upwardly facing surface of the annular shoulderdefined around and having a sliding relation with the upper end portionof the anvil element 15. The top cylinder head area facing the surface13b of the hammer is made up of the downwardly facing surfaces of thevalve composition occupying the upper end of the cylinder. Foridentification, the annular bottom and aggregate top cylinder headsurface areas are respectively denoted with the numbers 12a and 12b.

The anvil 15 has an enlarged intermediate portion 15a that sealinglyreciprocates within an anvil chamber 16, and the anvil chamber has lowerand upper end closures 16a and 16b which respectively engage the lower aplurality of angularly spaced ports 17c, and communicating at its lowerend with the anvil chamber through an annular space 210 (the function ofwhich will be described in greater detail hereinafter) and a pluralityof flow passages 17d associated therewith. Therefore, the lower endportions of the anvil chamber 16 and cylinder 12 are necessarilypressurized simultaneously to substantially the same value.

The upper end portion of the anvil chamber 16 adjacent the end closure16b thereof is exhausted to atmosphere through a passage networkcomprising a plurality of interconnecting passages 18a, 18b andextending through the anvil 15. The passage 18c opens into a chamber180! that receives therein both the bottom end portion of the loweranvil stem and the upper interior end portion of a steel spike or workmember 19 slidably carried by the casing 11 for limited axial movementswith respect thereto. Since the spike 19 defines a loose slidable fitwith the related walls of the casing, the chamber 18d is maintained atatmospheric pressure and, therefore, the upper end of the anvil chamber16 is also continuously maintained at atmospheric pressure. The bottomsurface of the lower anvil stem (which extends through the surface 16aand is sealingly related thereo) is adapted to rest upon the upper innerend of the spike 19 which may be a conventional hexagonal work memberhaving a pointed lower end and an outwardly extending annular retainingflange 19a adapted to cooperate with a retainer element 19b threadedlymounted upon the casing 11 at the lower end thereof. Thus the spike 19is removably constrained in the casing by the retainer element 19b forlimited axial displacements.

In operation of the structural arrangement thus far described, andassuming initially a parts configuration in which the hammer 13 is inabutment with the upper surface 15b of the anvil, a charge of compressedair will be directed by the valve composition 12' into the lower endportion of the cylinder 12 through the passage 17a in the tool casing.Such charge of air acting upwardly upon the bottom surface 131: of thehammer will reciprocate the hammer upwardly through the return strokethereof. Simultaneously, however, a reactive pressure force actingdownwardly upon the lower reaction surface (the terms lower reactionsurface and upper reaction surface respectively designating the totalupwardly facing and total downwardly facing surface areas reactivelypressurized by the charges of air reciprocating the hammer, and whichrespectively transmit downwardly directed and upwardly directed axialforces to the casing; and which in the subject structure respectivelycomprise the aforesaid surfaces 12a and 16a, and the aforesaid surface12b) will tend to cause the casing 11 to vibrate downwardly as thehammer 13 is reciprocated through its return stroke, and such reactivepressure force is applied to the casing until the upwardly moving hammerpasses the port 14a of the exhaust composition 14, at which time thelower end portion of the cylinder 12 as well as the lower end portion ofthe anvil chamber 16 will be exhausted to atmosphere.

As the hammer 13 approaches the upper end closure of the cylinder 12,the valve composition 12' directs a charge of compressed air into theupper end portion of the cylinder, and the resulting pressure forceacting downwardly uponthe hammer reciprocates it into impact with thesurface 15b of the anvil which transmits such impact to the spike 19.Simultaneously, however, such charge of compressed air exerts anupwardly directed reactive force against the upper reaction surface ofthe casing or of the cylinder defined thereby which tends to vibrate thecasing upwardly, and such reaction force is applied to the casing untilthe downwardly moving hammer 13 passes the exhaust port 14a, at whichtime the upper end portion of the cylinder 12 is exhausted toatmosphere.

Since the reciprocatory frequency of the hammer in a conventionalvibratory tool may approach and exceed 1,200 cycles per minute, thecasing thereof would objectionably vibrate longitudinally at the samerapid rate; but with reference to the present invention, theaforementioned counterbalancing system is effective to nullify thereactive pressure forces that normally cause such casing vibration; andthe structural arrangement accomplishing this counterbalancing in thetool of FIGURE 1 will now be described.

Operative in the main tool casing 11 is an annular oscillator 20reciprocable in its own cylinder 21. This oscillator element 20comprises a massive body or piston portion having annular shoulders orpiston surfaces 20d and 2% which are reciprocable relative to and incoaxial relation with the respectively opposing annular cylinder headsurfaces 21a and 21b carried by the casing (respectively denotedhereinafter as upper and lower counterbalancing surfaces).

It will be observed in the drawings that the oscillator cylinder 21, andmore particularly the variable-volume annular space 21c thereof definedbetween the upper piston and cylinder head surfaces 20d and 21a,connects by the tube or passageway 17, annular space 17b and ports 170to the variable-volume space under the hammer 13 in the main cylinder12. Similarly, the lower variablevolume space 21d in the oscillatorcylinder and the variable-volume space above the hammer 13 in the maincylinder 12 are connected by a tube or passageway 22.

Before describing the operation of the tool with reference to thepressure-force counter-balancing system, it should be noted that theaxially projected areas of the upper reaction surface 125 in the maincylinder 12 and the lower counter-balancing surface 21b in theoscillator cylinder 21 are substantially equal, and similarly, that theaxially projected areas of the lower reaction surface (12a plus 16a) inthe main cylinder 12 and the upper counterbalancing surface 21a of theoscillator cylinder 21 are substantially equal, for such conditions ofequality provide the most ideal functioning of the pressure-forcecounterbalancing system. In the specific tool structure considered, anadditional equality is present in that the axially projected areas ofthe lower and upper surfaces 13a and 13b of the hammer are substantiallyequal, and approximately equal thereto are the axially projected areasof the lower and upper reaction surfaces.

Considering again the operation of the tool, and assuming the sameinitial condition thereof, the admission of a charge of compressed airbeneath the hammer to reciprocate the same upwardly, and whichnecessarily applies a downwardly directed reactive pressure forceagainst the casing, will simultaneously apply an upwardly directedpressure force against the casing or, more specifically, against theupper counterbalancing surface 21a thereof, because of theinterconnection of the upper end portion 210 of the oscillator cylinderwith the lower end of the cylinder 12 through the passage 17, chamber171) and ports 170. Since the axially projected areas of the uppercounterbalancing surface 21a and the lower reaction surface areapproximately equal, the upwardly and downwardly directed pressureforces applied simultaneously to the casing are substantially equal and,therefore, counterbalance and effectively eliminate downward vibratorymovement of the casing which would otherwise result f-rom the admissionof compressed air into the lower end portion of the cylinder 12 toreciprocate the hammer 13 upwardly.

correspondingly, when a charge of air is introduced into the upper endportion of the cylinder 12 to reciprocate the hammer 13 downwardly, thereactive force acting against the upper reaction surface of the casingand which tends to vibrate the same upwardly is counterbalanced by thesimultaneous application of a downwardly directed pressure force uponthe casing or, more specifically, against the lower counterbalancingsurface 21b because of the interconnection of the lower end portion 21dof the oscillator cylinder with the upper end portion of the cylinder 12through the passage 22. Since the axially projected areas of the upperreaction surface of the cylinder 12 and the lower counterbalancing 21bof the oscillator are substantially equal, the reactive pressure forcewhich would otherwise vibrate the casing 11 upwardly is effectivelycounterbalanced.

It will be apparent that the counterbalancing action requires phases ofoperation during which each of the surfaces 21a and 21b is pressurizedwithout the other of these surfaces being simultaneously pressurized;and in terms of structure, this requirement defines the condition thatthe oscillator 20 be a hermetic barrier interposed between the surfaces21a and 21b to maintain pneumatic isolation therebetween. It is furtherevident that the oscillator 20 in this environment is necessarilysubjected to reversing forces of a substantial order of magnitude, andmust be supported within its cylinder with a positional stability suchthat it is maintained intermediate the ends of the cylinder in anon-impacting relation therewith so as not to transmit anyuncounterbalanced variable forces to the casing.

The structural arrangement for accomplishing this condition ofpositional stability includes a piston 23 extending upwardly from thetop of the oscillator 20. A cylinder 24 that slidably receives thepiston 23 is provided with escape holes 25a permitting the cylinder toexhaust to atmosphere, and the uncapped upper end 24a of the cylinderopens into an annular tank 26 defining a constant pressure space 2'7therein. Each of the escape holes 25a leads into an annular space 25bdefined about the cylinder 24 and such annular space is loosely coveredby a dust seal but is maintained at atmospheric pressure. Each of theescape holes 25a is equipped with a spring biased valve 250 which, alongwith the annular space and dust shield, are optional features andfunction to prevent the pressure in the cylinder 24 and constantpressure space 27 from dropping below arelatively low predeterminedvalue (for example, 3 pounds per square inch gauge) sufficient to holdthe oscillator 20 in its downmost position when the tool is not running,which prevents the first upward oscillations of the oscillator fromcarrying it into impact with its own upper cylinder head 21a.

Air is supplied to the constant pressure space 27 through a restrictedpassage or inlet orifice 29 that communicates through a passage 30,recess 39a, annular channel 36b and passage Site with the passage 12" inthe handle T upstream of the trigger valve 12 Thus, the constantpressure space 27 is continuously supplied with compressed air(substantially reduced beolw line pressure because of the restriction29) irrespective of whether the tool is running. Preferably a valve (notshown) located along the conduit H, or at the compressor or othersource, is used to terminate the flow of air to the constant pressurespace during periods of relatively long inactivity of the tool.

The escape holes 25a, collection space 25b and valve 25c togethercomprise the exhaust system for the space 27, and this exhaust system,together with the restricted infeed orifice 29 and piston 23 actingcooperatively therewith in a manner described hereinafter, comprises theaforementioned automatic control system whereby the aforesaid conditionof positional stability is imposed upon the oscillator 20.

This composite automatic control system is pneumatically energized by ahigh pressure inflow through the restricted orifice 29, which generallyeffects a substantial pressure drop, and into and through the compositespace consisting of the constant pressure space 27 and space in theupper portion of the cylinder 24, to commence its escape therefrom toatmosphere, whenever the position of the piston seal 231: permits,through the small ports 25a which collectively comprise a considerablygreater cross-sectional area than that of the inflow orifice 29. It maybe noted that the cylinder 24 need not necessarily have an open upperend as shown, which is the ideal condition, but any lesser openingconnecting the cylinder and constant pressure space 27 should besufficiently large so that substantially no pressure gradients willdevelop in the reciprocating air flow between the uper end portion ofthe cylinder and the constant pressure space.

The composite automatic control system is utilized to keep theoscillator from striking the cylinder heads 21a and 21b, and theprincipal tendency of the oscillator in this respect is to rise duringits oscillatory motion toward a condition of impact with the uppercyinder head 21a which may be explained in terms of the forces acting onthe hammer 13 as follows: First, the only forces acting downwardly uponthe hammer are the intermittently effective pneumatic forces (omittingthe force of gravity which is negligible and ineffective when the toolis operated in a horizontal position). Secondly, intermittentlyeffective pneumatic forces act upwardly upon the hammer, but in additionthere is a mechanical force which assists such upwardly acting pneumaticforces in urging the hammer upwardly. Such mechanical force is caused bythe impact relation of the hammer and anvil for when the hammer strikesthe anvil, the anvil is urged downwardly for an extremely brief intervalby an extremely large force which may approach a value of 50,000 pounds.Action and reaction being equal, the hammer is urged upwardly by thisvery large force.

These considerations establish that the average value of the pneumaticforces acting upwardly on the hammer must be less than the average valueof the pneumatic forces acting downwardly thereon inasmuch as the meanposition of the hammer remains fairly fixed during operation of thetool; for, since the hammer does not migrate beyond the limits of itscylinder during operation of the tool, it is necessarily implied thatthe respective average values of all of the forces acting downwardly onthe hammer and of all of the forces acting upwardly thereagainst arevery closely equal; whence, more specifically, the average value of thetotal pneumatic and mechanical force acting upwardly upon the hammermust be almost exactly equal to the average value of the pneumatic forceacting downwardly thereagainst; so that it follows that the averagevalue of the pneumatic forces acting upwradly against the hammer must besubstantially less than the average value of the pneumatic forces actingdownwardly thereon.

Since the space 21c above the oscillator is in open communication withthe space in the cylinder 12 below the hammer, and the space 21d belowthe oscillator is in open communication with the space in the cylinderabove the hammer, the average values of the pressures in theseoscillator spaces are substantially equal respectively to the averagevalues of the pressures in the cylinder spaces below and above thehammer. Therefore, in consequence of the foregoing argument, there is aneffective preponderance of the average value of the pneumatic forceacting upwardly upon the oscillator over the average value of thepneumatic force acting downwardly thereon, which imposes upon theoscillator a continuous tendency to rise which, if not arrested, wouldreintroduce vibration into the casing 11 since the oscillator wouldpound against the upper cylinder head surface 211:.

To prevent this, an additional surface is employed on the oscillatoragainst which sufficient pressure can be developed to hold theoscillator down whereby it can be made to operate over a reciprocatoryrange intermediate the ends of its maximum stroke so that it will notstrike the cylinder heads 21a and 21b respectively above and below theoscillator, and such additional surface is the top surface of the piston23 in the automatic control system comprising the previously specifiedelements 29, 25a, 25b, 25c and 23a, together with the piston 23 and thecontinuous space within the tank 26 and cylinder 24.

This composite structure operates so that if the oscillator 20 starts tooscillate about a mean position which is too high, thereby causing adanger of impact with the cylinder head 21a, the piston 23 will riseupwardly with the oscillator and will close the escape holes 25a, asseen in FIGURE 1. The establishment of this condition prevents escape ofair from the total space above the piston 23, and the compressed aircontinuously fed into this space through the restricted inlet orifice 29will cause the pressure therein to increase in value and, as aconsequence, the oscillator 20 will be urged downwardly with a steadilyincreasing pressure force until it reaches a position in which theescape holes 25a are uncovered during at least part of reciprocatorycycle of the oscillator. If the oscillator is forced downwardly untilthe escape holes remain uncovered during the entire reciprocatory cycleof the oscillator, the pressure within the space above the piston 23will drop rapidly. The pressure will then continue to decrease until itno longer gives sufiicient assistance to the pressure force acting onthe surface 20d of the oscillator to hold it in such lower position, andthe oscillator will then start to rise toward its stable intermediatelocation in which the escape holes are covered during a part of eachcycle of reciprocation.

Experience has shown that migration of the oscillator such that theescape holes are either closed or open during the entire reciprocatorycycle of the oscillator is held to brief durations, and there istherefore a strong tendency for the oscillator to remain stabilized inan intermediate location wherein the escape holes are closed during onlya part of each reciprocatory cycle of the oscillator. It should beunderstood that successful operation of the automatic control in thisparticular structural design requires compensatory changes in thepressure acting downwardly on the surface of the piston 23 to beeffected quickly since the average value of the mechanical impact forcereactively delivered during any relatively short interval by the anvil15 upwardly against the bottom of the hammer 13 is related to thestrength and elastic properties of the concrete being encountered by thespike 19 during that same interval, and such qualities of the concreteare subject to rapid variations. It will be apparent that the purpose ofthe relatively large pressurized space comprising the space 27 and spacewithin the cylinder 24 in communication therewith, as compared to thecyclic displacements of the piston 23, is to assure that the value ofthe force present in the force-transmitting linkage defined by the aircolumn connecting the casing structure and oscillator will remainsubstantially constant during each cyclic displacement of the oscillatorso as to invest such force-transmitting linkage with the valuableincapacity to transmit vibration between two bodies necessarilyinterconnected thereby, being respectively an unavoidably vibratingbody-namely, the oscillator 20and a body in which the occurrence ofvibration is objectionable namely, the oscillator cylinder and otherelements of the composite casing structure.

As heretofore indicated, the axially projected area of theupwardly-facing lower pressurizable surface 16a of the anvil chamber 16is substantially equal to the area of the upwardly-facing,impact-receiving surface 15b of the anvil 15. Evidently, then, thedownwardly-facing pressurizable surface at the lower end of the enlargedintermediate section 15a of the anvil has substantially the same axiallyprojected area as that of the surface 16a; and, therefore, theupwardly-facing surface 15b of the anvil and the downwardly-facingsurface at the lower end of the anvil section 15a are substantiallyequal to area. Consequently, and because the lower end portion of thecylinder 12 and lower end portion of the anvil chamber 16 are connectedto each other by the passage 17, chambers 17b and 21c, and ports 17c and17d, such lower end portions of the cylinder 12 and anvil chamber 16 aresimultaneously pressurized and the respective pressures therein arenecessarily of substantially equal value. This interrelationship definesa compensated anvil and the function and advantages thereof aredescribed in detail in the aforementioned Patent No. 3,028,841, to whichreference may be made for a complete description of such feature.

For convenience herein, however, it may be stated in general terms thata compensated anvil has the advantage of eliminating the waste ofdownpush momentum supplied to the tool (and delivered through the spikethereof to the concrete slab) that results from the conventionallyemployed expedient of attempting to firmly seat the anvil of the toolupon the upper end of the spike thereof at the moment of the delivery ofimpact to the anvil by the downwardly accelerating hammer-pistonsuchexpedient being pressurization of the upwardly-facing, impact-receivingsurface of the anvil to develop a downwardly-acting force thereontending to move the anvil downwardly relative to the tool casing andinto abutment with the upper end of the spike. The downpush momentumwasted by pressurizing the anvil to create a downwardly-acting forcethereon between the intervals of impact is obviated in the compensatedanvil structure by pressurizing the downwardly facing surface of theintermediate section 15a of the anvil simultaneously with thepressurization of the upwardly-facing surface 151) thereof. Thereforethe simultaneously-applied, equal-valued pressure forces actingdownwardly upon and upwardly against the anvil substantially cancel eachother since they are of equal value and no net downward force, and nowaste of downpush momentum, are then wastefully transmitted totheconcrete slab.

The desirability of having the anvil firmly seated upon the upper end ofthe spike at the moment of impact is to avoid what can be termedrattling or bouncing degeneration of the blow energy. More particularly,it has been found in the demolition of concrete that any specific amountof blow energy delivered to the spike is much more effective for drivingthe spike into the concrete if concentrated into a single blow than ifsubdivided into a great number of weaker blows totaling the same amountof energy. In view of the almost perfect elasticity of the steel anviland hammer-piston components, the action which follows the delivery of ablow by the typically much heavier hammer to the relatively light-weightanvil when the anvil is caught by the hammer in a midair position (i.e.,not sea-ted upon the spike but spaced upwardly therefrom) is as follows:

First, the anvil will bounce downwardly from such rnidair position offof the bottom surface of the hammer with a velocity considerably higherthan the hammer velocity (just as a highly elastic golf ball bounceswith greater velocity off the advancing face of a golf club).

Second, by virtue of this greater downward velocity of the anvil, itwill arrive at and bounce upwardly off of the upper end of the spikewhile the more slowly descending hammer, further reduced in speed byhaving thus elastically transmitted aportion of its energy to the anvil,is still at a relatievly considerable distance above it.

Third, the anvil, in consequence of thus bouncing upwardly off thespike, will return to meet and again impact with the hammer in asomewhat lower new midair position, after where there will be severalrepetitions of such sequential bouncing action between the hammer andanvil to define a number of successively lower midair positions of thissort.

Inasmuch as each repetition of such sequential bouncing action entailsthe delivery by the thus rapidly vibrating anvil of one impact upon thespike, transmitting thereto a parcel of energy obtained from the totalamount of kinetic energy contained in the descending hammer before itsinitial impact with the anvil in its first-mentioned midair position, itis obvious that the described repetitive bouncing process causes thatspecific amount of blow energy to be subdivided into a number of weakerblows totaling the same amount of energythus, as hereinbefore stated,re-

it) ducing the effectiveness of the total blow energy so subdivided fordriving the spike into the concrete.

In the conventional vibratory tool structure, the aforementionedexpedient of pressurizing the anvil to seat the same upon the upper endof the spike is extensively employed because it is virtually impossibleto utilize the violently vibrating casing for this purpose by bringingthe same (or a downwardly-facing surface of the anvil block providedtherein) into firm abutment with an upwardlyfacing, associated surfacedefined by the anvil for the purpose of pressing the anvil downwardlyand into such seating engagement with the spike. In the tool structurebeing considered herein, the casing is substantially vibrationless, and,as a result, a workman can continuously control the casing 11 and theanvil 15, and can seat the latter upon the upper end of the spike 19.

in addition to this advantageous compensated anvil feature, the toolstructure illustrated in FIGURE 1 comprises an anvil and hammer-pistonrelationship that maximizes the transfer of energy from thehammer-piston to the anvil by what may be termed a billiard ball effect.More specifically, the anvil 15 and hammer-piston 13 have thecharacteristic of effecting a substantially complete transfer of all ofthe kinetic energy of the downwardly-accelerating hamer-piston to therelatively stationary anvil upon impact of the hammer-piston with theanvil. The proper design of such components to effect this resultresides in assigning proper mass-distribution relationship thereto.

More particularly, such relationship comprises two terms; namely, weightand shape, and of the two weight is ordinarily by far the dominant term.Therefore, in the tool shown in FIGURE 1 the anvil and the hammer-pistonhave substantially equal weights, and the shapes thereof have the samegeneral order of similitude although the anvil is somewhat greater inaxial length than the hammer-piston and is also somewhat smaller inaverage diameter. Both dimensions are of the same general order and forthe purpose of the aforementioned relationship, are well within thepermissible range of variation. Therefore, since the weights of thehammer-piston 13 and anvil 15 are substantially the same, the shapesthereof are sufficiently similar, and both are almost perfectly elasticelements, impact of the hammer-piston against the anvil will result in asubstantially complete transfer of the blow energy from the hammer tothe anvil with the result that the anvil will be almost instantaneouslyaccelerated downwardly and the acceleration of the hammer will becorrespondingly reduced to zero, i.e., it will be essentially stoppedupon impact.

Such energy transfer will be effected irrespective of Whether the anvil15 is firmly seated upon the upper end of the spike 19 and, therefore,the energy transfer from the hammer to the anvil will be much greaterthan in prior structures even if the anvil is in a midair position. Inthis latter instance, the anvil, in effect, becomes the hammer elementafter impact thereof with the hammer 13 and delivers the blow energytransferred thereto to the spike 19 by impact therewith. However, thetransmission of impact energy from the hammer-piston 13 to the spike 19will, in general, be more complete and perfect if the anvil 15 is seatedupon the spike at the moment of its impact with the hammer-piston. Insome instances it may be desirable to have the weight of thehammerpiston 13 slightly less than the weight of the anvil 15 in orderto prevent the anvil from rebounding upwardly and into impact engagementwith the casing which could introduce an undesirable vibratory motionthereto.

More particularly, it has been found that the spike 19 sometimes tendsto be accelerated upwardly as a consequence of recoil forces operativethereagainst which, at least in part, are belived to be caused by thecomposition of certain concretes. For example, it is known that aconsiderable portion of the impact energy delivered to the spike 19appears as heat developed between the spike and the concrete slabresisting penetration by the spike. It is postulated that the moisturecontent of certain concrete compositions is such that pockets of steamare caused under the spike by the heat developed between it and theconcrete slab, and upon occasion, conditions are such that the resultingsteam pressure causes the spike to recoil upwardly. When this conditionoccurs, the spike jumps upwardly and transmits such motion to the anvilwhich in turn is propelled upwardly and into impact engagement with thecasing.

If the weight of the hammer 13 is slightly less than that of the anvil15, it will tend to be accelerated upwardly at a very slow rate byimpact thereof with the anvil; and if such upward acceleration of thehammer is sufiiciently slow, the anvil 15 which has been acceleratedupwardly by the aforementioned recoil force will then strike theupwardly-moving hammer and most of the energy then contained by theanvil will be transmitted to the hammerpiston further tending toaccelerate it upwardly. As a consequence, the upward motion of the anvilwill be terminated or slowed sufficiently so that any subsequent impactthereof with the casing will transmit a negligible force thereto.

The casing composition 11 comprises an inner casing element 11a and anouter casing element 11b coaxially circumjacent thereto. The outercasing elements is equipped with the handles T at its upper end, carriesthe retainer element 19b at its lower end, and is of generally tubularor cylindrical configuration having an axially extending hollowinterior. At its upper end the outer casing element is provided withinternal threads 11c that matingly engage external threads provided by aclosure cap or plug 11d.

The plug 11d bears downwardly upon the upper end of the inner casingelement 11a to seat the lower end thereof upon an inwardly steppedannular shoulder He provided by the outer casing element adjacent thelower end portion thereof. For convenience in machining the inner casingelement, it is divided into two sections, as shown at 11), and suchsections are maintained in the position shown, and the entire interiorcasing element maintained in a condition of compression, by thecompressional force applied to the opposite ends thereof by the outercasing through the shoulder He and plug 11d. Quite apparently then, theouter casing element 11b is necessarily in a condition of tension and itis, in effect, a spring element maintaining the upper and lower sectionsof the inner casing component in a unitary state.

The tool is assembled by inserting the inner casing element 1111 intothe hollow interior of the outer casing element 11b through the openupper end thereof; and the anvil 15, anvil block surrounding the upperstem of the anvil, hammer piston 13, and valve composition 12a areinserted into the interior of the inner casing element 11a, in the orderstated, through the open upper end thereof which is occupied by thevalve composition 12a in the illustration of FIGURE 1. The anvil blocksurrounding the upper stem of the anvil 15 is rigidly constrained in theposition shown by a tubular sleeve 11g telescopically received withinthe inner casing element and forming the annular wall of the cylinder12. The sleeve, or cylinder liner 11g, is pressed downwardly and intoengagement with the anvil block by the cap 11d which resiliently bearsdownwardly upon the valve composition 12a through the helical springshown, and the valve composition seats upon the upper end of the sleeve11g to urge the same downwardly. At its lower end the valve block seatsupon an annular shoulder 1111 provided by the inner casing elementadjacent the upper end portion of the anvil chamber 12; and, therefore,the anvil block and sleeve are both constrained within the inner casingelement.

The exhaust system 14 for the main cylinder 12 includes a plurality ofangularly spaced ports 140 provided in the sleeve 11g and such portsrespectively communicate with a plurality of angular spaced, axiallyextending grooves 14b cut in the inner casing element 11a, and each suchgroove opens into a pair registering ports 14c extending transverselythrough the inner and outer casing elements. The grooves 1411 are closedinteriorly by the circumjacent sleeve 11g.

The constant pressure space 27 is defined by a pair of axially-elongatedannular channels respectively out along the inner surface of the outercasing element 11b and the outer surface of the inner casing element11a. Such channels are disposed in facing relation when the casingelements are assembled to form the constant pressure space. It will beapparent that the oscillator or oscillatory mass member 20, which is acontinuous, unitary annular component may be formed integrally with thecontrol piston 23, as shown, and that such component must be insertedinto the outer casing element either prior to or at the same time thatthe inner casing element is inserted thereinto. Quite evidently, thepiston 23 as well as the oscillatory mass member may be equipped withrings or other seal elements to effect a good sealing relation with theslidably engaged surfaces of the inner and outer casing elementsif suchseals are either necessary or desirable.

The various flow passages formed in the inner and outer casing elementsmay be drilled or otherwise provided by conventional techniques, andplugs are used where necessary to close access openings formed by suchboring operations. Such plugs have been largely omitted in the drawingfor the purpose of simplifying the same. As shown most clearly in FIGURE2, the flow passage 22 is formed in an axially extending boss orenlargement provided by the outer casing element 11b along one sidethereof; and in the structure of FIGURES 1 and 2, such lateralenlargement is located below the laterally extending handles T which insome instances may be inconvenient or undesirable. Since the angularlocation of the passage 22 and easing enlargement containing the same isin no sense critical, both may be located wherever convenient such, forexample, as shown in FIGURE 3 wherein both the enlargement and bore areoffset by approximately from the position thereof shown in FIGURE 2. Inother respects the modified structure shown in FIGURE 3 is identical andfor this reason the primed form of the same numerals are employed todesignate the respectively corresponding parts.

Wherever appropriate enlarged ports, 30a for example, and annularchannels such as 12h and 30b may be used to facilitate registration ofthe various interconnecting ports, passages and other air-flow spaces;and appropriate registration of the upper and lower sections of theinner casing element, of the sleeve 12g with the inner casing element,and of the inner and outer casing elements may be determined andenforced in any convenient and conventional manner as, for example, byindexing or polarizing pins and recesses.

It is evident that a number of pressurizable ports, passages, cylindersand other chambers or spaces are -defined between the circumjacent innerand outer casing of other contiguous surfaces where the occurrence ofleakage is undesirable are finished to close tolerances and may becoated with a thin layer of a suitable sealing or gasket compound (aconventional silicone-rubber gasket material, for example) prior to theassembly of the tool. As is customary in percussive tools, positive aircushions are provided where necessary to prevent metal-to-metal impact,except as between the hammer 13 and anvil 15 and as between the anvil 15and spike 19. An example of the provision for the establishment of onesuch air cushion is at the lower end of the cylinder 12 where the inletports 17c are seen to be located a substantial distance above thecylinder end closure 12a.

It should be noted that the oscillator 20, which is a rather massivecomponent, is located about a restricted portion of reduced outerdiameter of the inner casing element 11a and, consequently, the externaldiameter of the outer casing element 11b has not been increased toaccommodate the oscillator component. Therefore, the tool structure isrelatively small and compact, yet it may have a generally uniformdimension from the upper to the lower end thereof which is providedwithout having to arbitrarily increase the exterior diametral dimensionof the tool simply for the purpose of attaining such uniformity. Theoscillator cylinder is defined between the inner and outer casingelements, and the reciprocatory axis of the oscillatory mass member issubstantially coincident with the axis of reciprocation of the hammer13; and, therefore, the reciprocatory axes of the center of gravity ofthe oscillator mass is coincident with that of the hammer and no angularor torsional vibration is introduced into the tool structure by thereciprocatory motions of the oscillator.

While in the foregoing specification embodiments of the invention havebeen described in considerable detail for purposes of making a completedisclosure, it will be apparent to those skilled in the art thatnumerous changes may be made in those details without departing from theprinciples or spiritof theinvention.

I claim: v

1. In combination with a percussive tool having a casing provided with amain cylinder, work member structure carried by said casing for limitedaxial displacements with respect thereto, a hammer-piston axiallyreciprocable within said cylinder for the successive intermittentdelivery of impact force to said Work member structure, and means forreciprocating said hammer-piston by application of a reversing forcethereto reactively applied against said casing and tending to vibratethe same: said casing providing an oscillator cylinder therein coaxiallycircumjacent said main cylinder, an oscillatory mass member of annularconfiguration within said oscillator cylinder, means for applying tosaid oscillatory mass member to efiect reciprocation thereof a reversingforce which is reactively applied to said casing in opposition to theaforesaid reversing force whereby said casing does not vibrate as aconsequence of the reactive application of such reversing forcesthereto, means for developing a substantially continuous force operativeagainst said oscillatory mass member urging the same generally in thedirection of motion of said hammer-piston immediately prior to thedelivery of impact force thereby to said work member structure, andautomatic control structure responsive to the relative position of saidcasing and oscillatory mass member for varying the value of saidcontinuous force over a plurality of impact cycles of said hammer-pistonto maintain the range of reciprocatory movement of said oscillatory massmember relative to said casing within predetermined limits.

2. The percussive tool of claim 1 in which means are provided tomaintain said continuous force substantially constant during any oneimpact cycle of said tool.

3. The percussive tool of claim 1 in which the force tending toreciprocate said hammer-piston in a direction away from its impactrelation with said work member structure being in part impact reactionforce developed against said hammer-piston during the actual interval ofimpact thereof with said work member structure, said automatic controlstructure being operative to vary the valve of said continuous force inaccordance with changes in the average value of said impact reactionforce intermittently operatively against said hammer-piston to maintainthe aforesaid relation between said casing and oscillatory mass member.

4. The percussive tool of claim 3 in which means are provided tomaintain said continuous force substantially constant during any oneimpact cycle of said tool.

5. In a pneumatic percussive tool having a casing in which theoccurrence of vibration is undesirable and providing a main cylinder,work member structure carried by said casing for limited axialdisplacements with respect thereto, a hammer-piston axially reciprocableWithin said cylinder for the successive intermittent delivery of impactforce to said Work member structure, and means for reciprocating saidhammer-piston by the application of pneumatic pressures alternatelyagainst the opposite faces thereof whereby corresponding pneumaticreaction forces are alternately developed in opposite directions againstsaid casing tending to vibrate the same: said casing providing anoscillator cylinder therein coaxially circumjacent said main cylinder,an oscillatory mass member of annular configuration within saidoscillator cylinder and having oppositely oriented pressurizable faceshaving axially projected areas approximately equal to the similarlyprojected areas of the faces of said hammer-piston,means for applying tosaid oscillatory mass member for reciprocating the same pneumaticpressures alternately against the opposite faces thereof andcoordinately operative with said means for reciprocating saidhammer-piston so as to maintain a condition of substantiallysimultaneous equality between the values of the pressures respectivelyacting against the oppositely oriented faces of said hammer-piston andoscillatory mass member to continuously provide counteractive pneumaticreaction forces substantially nullifying the pneumatic reaction forcestending to vibrate said casing as a consequence of reciprocating saidhammerpiston, means for developing a substantially constant forceoperative against said oscillatory mass member urging the same generallyin the direction of motion of said hammerpiston immediately prior to thedelivery of impact force thereby to said work member structure, andautomatic control structure responsive to the relative position of saidcasing and oscillatory mass member for varying the valve of saidconstant force over a plurality of impact cycles of said hammer-pistonto maintain the range of reciprocatory movement of said oscillatory massmember relative to said casing within predetermined limits.

1 6. The percussive tool of claim 5 in which said means for developingsaid substantially constant force includes a pair of relativelyreciprocable opposed surfaces respectively provided by said casing andoscillatory mass member, a pressurizable enclosure defined about saidsurfaces, and means for establishing a gaseous column within saidenclosure operative between said opposed surfaces, and in which saidautomatic control structure includes means for admitting gas underpressure to said enclosure, means for permitting the escape of gastherefrom, and means for regulating the relative rates of such supply ofgas to and escape of gas from said enclosure.

7. The apparatus of claim 5 in which the weights of said hammer-pistonand work member structures are substantially equal so that substantiallythe entire kinetic energy content of said hammer-piston is delivered tosaid work member structure upon impact of said hammerpiston therewith.

References Cited by the Examiner UNITED STATES PATENTS 534,812 2/1895Carlinet l73l28 X 1,802,987 4/1931 Shook 173l03 3,028,841 4/1962 Leavell173l39 X 3,060,894 10/1962 Dean et al 173139 X BROUGHTON G. DURHAM,Primary Examiner.

L. P. KESSLER, Assistane Examiner.

1. IN COMBINATION WITH A PERCUSSIVE TOOL HAVING A CASING PROVIDED WITH AMAIN CYLINDER, WORK MEMBER STRUCTURE CARRIED BY SAID CASING FOR LIMITEDAXIAL DISPLACEMENTS WITH RESPECT THERETO, A HAMMER-PISTON AXIALLYRECIPROCABLE WITHIN SAID CYLINDER FOR THE SUCCESSIVE INTERMITTENTGDELIVERY OF IMPACT FORCE TO SAID WORK MEMBER STRUCTURE, AN MEANS FORRECIPROCATING SAID HAMMESR-PISTON BY APPLICATION OF A REVERSING FORCETHERETO REACTIVELY APPLIED AGAINST SAID CASING AND TENDING TO VIBRATETHE SAME: SAID CASING PROVIDING AND OSCILLATOR CYLINDER THEREINCOAXIALLY CIRCUMJACENT SAID MAIN CYLINDER, AN OSCILLATORY MASS MEMBER OFANNULAR CONFIGURATION WITHIN SAID OSCILLATOR CYLINDER, MEANS FORAPPLYING TO SAID OSCILLATORY MASS MEMBER TO EFFECT RECIPROCATION THEREOFA REVERSING FORCE WHICH IS REACTIVELY APPLIED TO SAID CASING INOPPOSITION TO THE AFORESAID REVERSING FORCE WHEREBY SAID CASING DOES NOTVIBRATE AS A CONSEQUENCE OF THE REACTIVE APPLICATION OF SUCH REVERSINGFORCES THERETO, MEANS FOR DEVELOPING A SUBSTANTIALLY CONTINUOUS FORCEOPERATIVE AGAINST SAID OSCILLATORY